Having campaigned for the Oscar on the platform that she should receive it as a symbolic reparation to all the African-American actresses before her who had not won it, Berry exulted, "It's for every nameless, faceless woman of color who now has a chance because this door tonight has been opened." Yet, at about that point, ABC flashed a quick shot of the ex-beauty queen's mother, who is a blonde white woman.

In America's complex racial system, there isn't much about blacks and whites that is completely black or white.

This begins a series of three articles on an important, but seldom rigorously analyzed facet of the American people: What population geneticists call the "admixture" of the races. Data from new sources now allows a much more revealing picture of racial mixing in the U.S. than was possible until very recently.

The issue has political, significance: University of California regent Ward Connerly, the leader of the victorious 1996 Propoition 209 initiative campaign to outlaw racial preferences in that state, has collected enough signatures to get on the ballot a new proposal that he calls the Racial Privacy Initiative. (It's uncertain whether it will be on the 2002 or 2004 ballot.)

It would ban most uses of racial classifications by the state of California. In its first Field Poll, likely voters favored the Racial Privacy Initiative almost three to two.

Although Connerly is almost always labeled "black," he points out that he is actually black, white, and American Indian. And he has grandchildren who are Asian as well. He believes that racial classifications are outmoded and divisive.

An ongoing genetic study of black-white admixture conducted by molecular anthropologists at Penn State University has for the first time confidently answered old questions about how intermingled are the family trees of African-Americans and European-Americans.

The third article will examine a striking contrast to America's racial structure: the nearly total disappearance of Mexico's African-looking people. In colonial Mexico's 1810 census, a tenth of the population was labeled "Afro-Mexican." What happened to them?

Another new data source is providing a different but also informative perspective on racial mixing in the U.S. In 2000, for the first time, the Census allowed Americans to designate themselves, or their children, as being of more than one race.

The old "One Drop of Blood" rule, which said that anyone who has any black ancestry is African-American, appears to be eroding finally. The Census found that among people over age 65 who called themselves at least part black, a mere two percent said they were also some other race. (This will be referred to as the "black and other" percentage.) In contrast, 12.6 percent of the newborns in 2000 who were at least partially black were (according to their parents) of more than one race. (To put this in perspective, 29 percent of babies who are at least partially Asian are of mixed race, according to the Census.)

This "black and other race" percentage appears to have doubled within the past dozen years. Among 10- to 13-year-old blacks, only 6.3 percent were called "black and other" by their parents or guardians.

What exactly do these "black and other" Census figures mean? They are quite different from Mark D. Shriver's genetic data, which show that -- at least outside of the rural South -- a large fraction of African-Americans possess some white ancestors.

In the United States, however, during Colonial times the rule became that any individual with "one drop" of African blood (or, alternately, at least one pure African great-grandparent) was to be considered black and nothing else.

There were exceptions: New Orleans famously tended to follow the more flexible and complicated Latin American system of racial classification. In general, though, all but the whitest-looking mixed race individuals were blocked from calling themselves anything but black. So, even today, most Americans of mixed black-white descent identify themselves on the Census as being only black.

According to demographer William H. Frey of the University of Michigan and the Milken Institute of Santa Monica, Calif., those who told the Census Bureau they were black and some other race typically have a non-black parent or grandparent. People who decide to go through the trouble of personally standing up to society's "one drop" rule generally do it to honor both their parents. Unlike Berry, many individuals with parents of different races protest that choosing just one parent's race would be disloyal to the other parent.

Most famously, Masters champion Tiger Woods ruffled the feathers of some blacks in 1997 by insisting that he was both black and Thai. (In fact, Woods sometimes uses the fanciful term he invented as a boy, "Caublinasian," to indicate that he is Cau-casian, black, Indian and Asian.)

Similarly, wrestler The Rock, star of the hit movie "The Scorpion King," is both black and Samoan.

In the 2000 Census, one of every eight new African-American babies was identified by his or her parents as being "black and other," compared to one of every sixteen 10-13 year olds. What does that mean? It presumably indicates that the number of offspring of mixed race matings has approximately doubled over the last dozen years.

Support for this comes in state-level data, which Frey recently published in a Milken Institute report. The "black and other" percentages of the black totals range from a low of 0.7 percent in heavily black Mississippi to 38 percent in nearly all-white Montana.

The "black and other" percentages of the various states correlates closely with the fraction of each state's population that identifies itself as African-American. According to a UPI statistical analyis of Frey's data, the black share of the state's population explains 87 percent of the differences in the "black and other" rate.

The chance that a black person will have a child with a person of another race is low in a state like Mississippi, where there are lots of other African-Americans around to pair up with. In Montana, however, where blacks are rare, African-Americans are more likely than in Mississippi to content themselves with a non-black mate. This consistent pattern suggests that for most blacks, a black mate would be their first choice.

The states that diverge somewhat from this pattern offer interesting clues about what drives interracial matings in modern America.

In Southern states, where the "one drop rule" had been most ferociously enforced, "black and other" individuals tend to be even rarer than one would expect judging from their large black share of the population. Frey noted, "The identification of blacks with their race is much more distinct in the South than in other parts of the country."

Other states with fewer than expected "black and others" include Illinois, where there is a high degree of residential segregation that keeps the races physically apart, thus discouraging interracial romance. Most blacks live in Chicago, while most whites live either in the city's suburbs or in the more rural Downstate area.

Another state with a lower than predicted "black or others" percentage is New Mexico, where the high proportion of Spanish-speakers and Indians on reservations lowers the proportion of children born to mixed race couples.

Even California, which is famous for its plentiful white-Asian interracial couples, does not have a particularly large number of "black and others." This is probably due to the state's large number of immigrants. According to a study by Sonya M. Tafoya of the Public Policy Institute of California, immigrants in the Golden State are only about one third as likely to marry interracially as native-born Americans. Language and cultural differences get in the way of cross-racial romance.

The most unexpectedly high percentage of "black and other" Census respondents is in Hawaii. The Aloha State has long enjoyed the highest overall rate of interracial marriage in the country. Further, many blacks in Hawaii moved there while serving in the armed forces. Service members are more likely to marry interracially than the general population. Alaska, another heavily military state, is also near the top of this list more mixed than expected.

Rhode Island and Massachusetts have far more "black and other" individuals than their black share of the population would indicate. This is driven in part by those two states' large numbers of Cape Verdeans. These are mixed race Portuguese-African islanders from a small island nation off the coast of West Africa.

Cape Verdeans are one of the few non-Hispanic populations who collectively consider themselves part black today. In contrast, the once self-consciously mixed race populations of New Orleans no longer show up in the Census. Although population geneticist Shriver found that New Orleans' black population does indeed have one of the higher white admixture rates in the country (22 percent), only one percent of Louisiana's African-American population identified themselves in 2000 as "black and other." The rise of black pride in the mid-20th century made unfashionable the discriminatory elitism of New Orleans' "octoroons" and "quadroons."

Politically and socially liberal states like Maryland, Minnesota, New York and Washington state also feature a greater than expected number of "black and others."